Early-state water migration characteristics of superabsorbent polymers in cement pastes

Water exchange and migration of superabsorbent polymers (SAP) in cement paste is a very complicated process and governs the effectiveness of internal curing in concrete. The early state of SAP in real pore fluids was investigated under different water-cement ratios and hydration time. It is found out water absorption of SAP is not a constant value, but varies depending on these two factors. The absorption and desorption behavior of SAP is demonstrated in the shifted hydration peak location and the water-rich region around the SAP gels. The water exchange between SAP and cement pastes is quantified by the measured water content with time, from which a characteristic “two-stage desorption” driven by osmotic pressure and humidity gradient, respectively, is identified. The humidity-controlled desorption that is beneficial for internal curing is calculated. It is indicated the internal curing efficiency could be improved by shortening the osmotic stage and prolonging the humidity stage.